Enhanced dielectric, thermal stability, and energy storage properties in compositionally engineered lead-free ceramics at morphotropic phase boundary

Abstract

Structural inhomogeneity at morphotropic phase boundary (MPB) offers a novel paradigm to explore and modulate the physical properties of dielectric materials to design next-generation multifunctional devices. In this work, two lead free materials at MPB; Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) and (Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNTBT), are combined together to synthesize polycrystalline composite samples of (1-x) BCZT-xBNTBT with x = 0.0, 0.25, 0.50, 0.75, and 1.0. Structural investigations using XRD show the coexistence of double phases for pristine BCZT (tetragonal (P4mm) + rhombohedral (R3m)), and for pristine BNTBT (tetragonal (P4bm) + rhombohedral (R3c)). However, all the doped samples with x = 0.25, 0.5, and 0.75 display a coexistence of triple phases with P4mm, P4bm, and R3c symmetries. Detailed dielectric study reveals a normal ferroelectric to macroscopic ergodic relaxor crossover for samples with x = 0.25 and 0.75. Intriguingly, sample x = 0.25 displays a coexistence of high dielectric constant (4050), ultralow dielectric loss (≤0.02), high temperature thermal stability of permittivity (variation ≤ ±15%) in a temperature range 135 °C–450 °C, large recoverable energy density (Wrec = 423 mJ/cm3) with ultrahigh energy storage efficiency (η = 95.4%) at low applied electric field - 23 kV/cm. Nevertheless, at similar applied field strength, the obtained values of Wrec and η exceed most of the selected lead-free energy storage materials. This work may pave a new path to design superior high-temperature dielectrics, through intermixing of MPBs, for energy storage applications.